The First Homologous Series of Self-Assembled Aryl Bromo- and Aryl Cyanocuprates, -Argentates, and -Aurates; MLi<sub>2</sub>XAr<sub>2</sub> (M = Cu<sup>I</sup>, Ag<sup>I</sup>, Au<sup>I</sup>; X = Br, C⋮N; Ar = [C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>N(Et)CH<sub>2</sub>CH<sub>2</sub>NEt<sub>2</sub>-2]<sup>-</sup>)
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Reaction of 2 molar equiv of the diamine chelated aryllithium dimers Li2(C6H4{CH2N(Et)CH2CH2NEt2}-2)2 (Li2Ar2) with the appropriate metal bromide allows the synthesis of the first homologous series of monomeric group 11 bromoate complexes of type MLi2BrAr2 (M = Cu (7), Ag (8), Au (9)). Both in the solid state and in solution, the bromocuprate 7 is isostructural with the bromoargentate 8. The crystal structures of 7 and 8 consist of a MLi2 core, and each of the two aryl ligands bridges via electron-deficient bonding between the group 11 metal and one Li atom (d(Cipso−M) = 1.941(4) (mean) and 2.122(4) (mean) Å, for 7 and 8, respectively). The bromine atom exclusively bridges between the two lithium atoms. Each of the ortho-CH2N(Et)CH2CH2NEt2 moieties is N,N‘-chelate bonded to one lithium (d(N−Li) = 2.195(5) and 2.182(0) (mean) Å for 7 and 2.154(8) and 2.220(1) (mean) Å for 8). Although the MLi2BrAr2 compounds are neutral higher-order -ate species, the structure can also be regarded as consisting of a contact ion pair consisting of two ionic fragments, [Li−Br−Li]+ and [Ar2M]-, which are interconnected by both Li-N,N‘-chelate bonding and a highly polar Cipso−Li interaction. On the basis of NMR and cryoscopic studies, the structural features of the bromoaurate 9 are similar to those of 7 and 8. A multinuclear NMR investigation shows that the bonding between the [Li−Br−Li] and [Ar2M] moieties is intermediate between ionic and neutral with an almost equally polarized Cipso−Li bond in 7, 8, and 9. Similar reactions between M(C⋮N) and 2 molar equiv of LiAr yield the analogous 2:1 cyanoate complexes of type MLi2(C⋮N)Ar2 (M = Ag (10), Au (11)). Multinuclear NMR studies show that the cyanoate complexes 10 and 11 are isostructural with the bromoate complexes 7, 8, and 9. This paper illustrates that these cyanoaurates may serve as excellent model complexes to gain more insight into the structure of 2:1 cyanocuprates in solution.
